Switching device with time-delay control



1951 H. A. G. HAZEU ET AL 2,536,548

SWITCHING DEVICE WITH TIME DELAY CONTROL Filed May 9, 1946 5 JOUKCE OF PULSA TING Lil I N V EN TORS. JH'NDRI'KAIZEVD GODAZZD [L422 U JO/MN M4215 ZIDEB 0H3 ATTORNEY Patented Jan. 2, 1951 SWITCHING DEVICE WITH TIME-DELAY CONTROL Hendrik Arend Godard Hazeu and Johan Marie Ledeboer, Eindhoven, Netherlands, assignors, by mesnc assignments, to Hartford National Bank and Trust Com trustee pany, Hartford, Conn., as

Application May 9, 1946, Serial No. 668,612 In the Netherlands February 18, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires February 18, 1962 7 Claims. 1

In various applications in electro-technics use is made of switching devices by which the current is switched on? at the correct moment in order to measure a quantity of energy required for a definite purpose. This switching off may take place after the current has circulated during a period of time adjusted beforehand or after an integral product of current, voltage or power and time, which has been adjusted beforehand, has been attained. The first case concerns a time switch and the second case, for example, a milliamperesecond relay. As the instrument for the determination of time may be utilized the combination of a condenser and a resistance. In the first case the charge of this condenser is modified by a current independent of the current to be switched off and in the second case by a current which is dependent upon the said current. Such switching devices are utilized, for example, in X-ray apparatus and in welding machines. For the sake of simplicity the following description always relates to the application to X-ray apparatus but the invention may also be carried into effect in other cases wherein use is made of such switching devices.

In addition to the circuit for the anode current of the X-ray tube, the principal circuit, an X-ray apparatus comprises an auxiliary circuit in which the current has to flow already for some time before the principal circuit is closed, viz. the circuit for the heating current of the cathode. There may also be more such auxiliary circuits; to them belongs, for example in the case of rotary anode tubes, the circuit through which flows the current by which the anode is set in motion. The auxiliary circuits are generally closed by one or more auxiliary relays, the principal circuit being closed by a principal relay. The exciting circuit of the principal relay is closed by or through the intermediary of the auxiliary relay. The principal relay functions, however, with a certain time-lag and switches in the anode current only some time after the auxiliary circuits have been closed.

The exciting current of the auxiliary relay is switched-in by the operator of the apparatus. Since the period of time during which this current remains switched-in must be independent of the period of time during which the actuating switch is kept closed, a switch conrolled by the auxiliary relay itself is connected into the circuit of the exciting current of the auxiliary relay in parallel with the actuating switch. When in the switch, which is generally constructed as an independently opening switch, for examples a push-button,

the contact is broken, the exciting current of the auxiliary relay, when the latter has once been closed, continues notwithstanding to flow so that this relay remains closed. The closure of the auxiliary relay results in that after a certain period of time during which the filament takes the required temperature and the rotary anode acquires the required number of revolutions, the principal relay is closed and is kept closed as long as is determined by the reviously selected adj ustment.

When the period of time adjusted has elapsed or the adjusted number of milliampere-seconds has been attained, the anode current is switched off, for example, due to the interruption of the exciting current of the principal relay. In the case of excitation by means of pulsatory current use may be made for this purpose of a thyratron whose grid voltage varies during the time of exposure owing to the variation in the charge of a condenser.

The switching device must operate in such manner that after the switching period has elapsed not only the principal relay but also the auxiliary relay is switched off since otherwise the switching-on and ofi of the principal relay would be repeated each time and since also the auxiliary circuits must be interrupted again. It is not sufficient to have the exciting circuit of the auxiliary relay interrupted by the principal relay when the latter switches off, for in this case it is no longer possible to close the exciting circuit of the auxiliary relay when the principal relay has been switched out of circuit.

The invention yields for this problem a solution owing to which, while avoiding additional relays which might constitute a source of disturbances, the switching device, after being utilized, is automatically brought each time into the state wherein it is again ready for being put anew into operation. For example with X-ray apparatus, it is thus avoided that a radiograph becomes a failure due to the fact that the operator omits to take beforehand the necessary steps, for example to throw-over switches, for making the switching device ready for use and does not perceive or perceives too late that the device does not function. The invention consequently meets the general endeavour to divert as little as possible the attention of the physician who operates the X-ray apparatus, by additional manipulations and to afford him the opportunity of paying its full attention to the medical work.

The invention will be explained more fully with reference to the accompanying drawing, wherein Fig. 1 represents the essential parts of the wiring diagram of one form of construction of a device according to the invention.

Fig. 2 represents the principal relay in another position and Figs. 3 and 4 show a modified form of construction of the principal relay in two positions.

Fig. 1 shows the auxiliary relay, constituted by a coil I and an armature 2, to which are secured contacts 3, t, 5 and 8. The coil is supplied by a source of current I. When a button 8 is depressed the exciting circuit of the coil I is closed, the armature of the relay being brought thereby into the position shown. Now the contact 3 closes, for example, the heating circuit of. the X-ray tube whilst the contact 4 closes the circuit of the current by which the rotary anode is set in motion. When the button 8 is released the current is not interrupted; for this purpose is provided the takeover contact 5 through which the exciting current of the coil l continues to flow. The contact 6 suppresses the short-circuit of a condenser 9. As soon as thi has taken place, this condenser is charged by a source of current l6 through a regulable resistance l l with the result that it acquires a steadily increasing voltage.

The positively charged electrode of the condenser 9 is connected, through a resistance l2 and a source of voltage 53, to the grid M of a thyratron IS. The cathode of this tube is connected to the negative electrode of the condenser 9. The source of voltage i3 initially supplied to the grid it so high a negative voltage that the tube could not be ignited, but the potential oi the grid steadily increases according as the condenser voltage rises and after some time, which time depends upon the values of the condenser 9 and of the resistance H, the grid voltage acquires a value at which the tube breaks down. If desired, the condenser 9 may have a variable capacity in order to be thus also enabled to regulate the time lag.

The tube It comprises furthermore a second grid i 8 which is connected through the intermediary of a source or" positive grid voltage il, a resistance l8 and a switch it to the cathode of the tube and consequently does not oppose the passage of current. Now a source of current 29, which provides pulsatory direct current, may send current through the tube l5 and through the coil 21 of the principal relay. The latter has a switch comprising a fixed contact ZZand a rotary contact arm 23. The latter is connected to an armature 24 which is raised by the coil 2! against the action of a spring 25 so that the contacts 22 and 23 are pressed against one another and the supply current of the X ray apparatus can flow through conductors 3i, and 32 The principal relay occupies in this case the position shown in Fig. l. The armature 24 also actuates the switch 89. Before this switch short-circuited a condenser 2'6. Now the condenser is charged by a source of direct current 2? through a variable resistance 2%. The polarity of the source of current 2? is such that that electrode of the condenser which is connected to the cathode of the tube becomes positive. The condenser voltage consequently counteracts the influence exerted by the source of voltage I l on the potential of the grid I6 and after a period of time whi ch depends on the value of the resistance 28 and on the capacity of the condenser 26, which condenser, if desired, may also be variable, thi potential takes so low a value that in the next voltage wave from pulsatory source 29 the tube can no longer be ignited and the excitation of the principal relay comes to an end. The switch is then drawn back by the spring 25 which brings the switch into the position in which it is shown in Fig. 2. Now the anode current of the X-ray tube is switched ofi and the switch 19 occupies the position in which the condenser 26 is short-circuited.

Now it would be possible for the tube It to be ignited anew but the construction according to the invention ensures that this cannot take place, for the exciting circuit of the auxiliary relay comprises an interrupter which is temporarily opened whenever the principal relay is opened. The period of time during which the interrupter is open must be at least equal to the time necessary for switching oil the auxiliary relay. It should not last longer than the time which may elapse between two exposures. These conditions can be easily satisfied. According to a further elaboration of the invention, one of the contacts of the interrupter is coupled for this purpose with a certain freedom of motion to the movable portion of the principal relay so that when the latter relay is switched off it is driven forward, leaves the other contact and, on account of its live force, acquires a deflection which is larger than that of the principal relay itself. Now the exciting circuit of the auxiliary relay is interrupted and the auxiliary relay returns to its out of service position. After having stopped the contact which has been driven forward is brought back to the ot e n a t y a force acting in the opposite direction. In the practical example of Figs. 1 and 2 the interrupter consists of two contact arms of which the one (29) is secured, if required so as to be electrically insulated, to the movable portion of the principal relay, the switch lever 23 whereas the other (36) is rotatable about the same shaft as the lever 23. When now the principal relay is opened, the loose contact arm 30 is driven forward by the contact arm 29 which is immovably mounted on the lever 23. When the switch of the principal relay and therefore the contact arm 29 comes to rest by means of a stop 3?, the loose contact arm 30 continues to move on account of its live force until it is brought back by anopposite force on the stationary contact arm 29 and occupies the position shown in Fig. 2. In this figure the deflection of the contact arm 35 is indicated by dotted lines.

The moment the switch 22, 23 is opened and the contact arm as has left the contact arm 29, th exciting circuit of the auxiliary relay is interrupted. Now the armature 2 moves into the position in which the contacts 3, 5 are broken and the condenser 9 is short-circuited by the contact 6. Due to the discharge of thi condenser the tube !5 can no longer be ignited. When the contact arm 35 falls back again on the contact arm 29, the exciting circuit of the coil i is no longer closed anew for at 5 the circuit has been interrupted meanwhile. The heating circuit and the other auxiliary circuits consequently remain Without current. The X-ra apparatus is now comple el a st a d o i t he fa t t t meanwhile the switch 29, 35 has been closed again, it is ready for the following exposure, which may be mad again simply by depressing the button 8. Due to the friction with which the contact arm 38 rotates on the shaft, its movement may be damped and its deflection may be regulated. For restoring it to the contact arm 29 use may be made of elasticity such as is provided b a spring 38 or of gravit Figs. 3 and 4 represent diagrammatically a further possibility of construction for the prin cipal relay. The principal switch is denoted by 33. The interrupter included, in accordance with the invention, in the exciting circuit of the auxil which starts rotating about the point 35. In con-.

sequence thereof it leaves the contact arm 35 so as to produce the interruption and acquires a defiection which is indicated in Fig. 4 by dotted lines. Then it falls back and is intercepted by the armature 2 2. Since the resilient arm 35 has meanwhile relaxed and its end lies at a slightly higher level, the two contact arms 3-3 and 3E touch one another also in the new position of the armature 3d and the interruption ceases, which was necessar in order to be able to put the switching device anew into operation by depressing the knob 8.

If after depression of the button 3 the latter is not released at once but is kept depressed until the complete switching operation has been terminated, the auxiliary relay would be drawnin at once when the interrupter 29, 3!} or 35 has done its duty, and the whole process would be repeated. This would lead to undesirable results if by mistake the knob were held fast too long.

What we claim is:

1. In a switching system, the combination coil.- prising an auxiliary relay provided with a winding and a normally-open first switch which closes upon energization of said winding, a voltage source connected through said first switch to said winding, an operator switch bridged across said first switch whereby closing of said operator switch effects energization of said auxiliary winding to close said first switch and maintain said winding energized, a principal relay provided with a winding, an interrupter switch and means responsive to the de-energization of the principal relay winding momentarily to open said switch, means responsive to the energization of the auxiliary relay winding to apply after a predetermined interval an energizing potential to the principal relay winding, means responsive to th energization of said principal relay winding to maintain same energized by said potential for a predetermined period, and means interposing said interruption switch between said source and said auxiliary relay winding whereby upon de-energization of said principal relay winding said auxiliary winding is also de-energized.

2. An arrangement, as set forth in claim 1, wherein said principal relay includes a pivotally mounted armature and means deflecting said armature upon de-energization of said principal relay winding, and wherein said interrupter switch is constituted by a first contact attached to said armature and movable therewith, a pivotally mounted second contact biased against said first contact and a stop member positioned to arrest the deflection of said first contact at a fixed point, whereby the second contact is driven forward to break contact momentarily and then by reason of said bias returns to said first contact.

3. An arrangement, as set forth in claim 2, further including spring means to bias said second contact against said first contact.

4. In a switching system, the combination comprising an auxiliary relay provided with a winding, a normally-open first switch which closes upon energization of said winding and a normallyclosed second switch which opens upon energization of said winding, a voltage source connected through said first switch to said auxiliary relay winding, an operator switch bridged across said first switch whereby closing of said operator switch effects energization of said auxiliary winding, a principal relay provided with a winding, a normally-closed third switch which opens upon energization of the principal relay winding, an interrupter switch and means responsive to the de-energization of the principal relay winding momentarily to open said interrupter switch, means responsive to the opening of said second switch to appiy after a predetermined interval an energizing potential to the principal relay winding, means responsive to the opening of said third switch to maintain the principal relay winding energized by said potential for a predetermined period, and means interposing said interruption switch between said source and said auxiliary relay winding, whereby upon deenergization of said principal relay winding said auxiliary winding is also ole-energized.

5. A system, as set forth in claim 4, wherein said means responsive to the second switch opening to apply fter a predetermined interval an energizing potential to the winding of the principal relay comprises a gaseous discharge tube having a cathode, at least one control electrode and an anode, a source of pulsating direct current connected between the cathode and anode of said tube through the winding of the principal relay, means connected to one control electrode to apply a cut-oi? bias thereto, and means including a time-delay network responsive to the opening of said second switch to impress an ignition voltage on said one control electrode, whereby said tube is fired and said principal relay winding energized.

6. A system, as set forth in claim 5, wherein said means to maintain said principal relay energized for a predetermined period comprising means including a time-delay network responsive to the opening of said third switch to apply an extinguishing voltage on another control electrode oi said tube.

'7. A system, as set forth in claim 6, wherein said principal relay and said auxiliary relay are each further provided with additional switches responsive to the energization of their respective windings for controlling external circuits.

HENDRIX AREND GODARD HAZEU. JOI-IAN MARIE LEDEBOER.

No references cited. 

